1. Field of the Invention
The present invention relates to an image sensor driving unit that orders an image sensor to rapidly discharge an unnecessary electrical charge generated by a charge-transfer channel, such as a CCD, before a photographing operation.
2. Description of the Related Art
Various kinds of image sensors that generate an image signal corresponding to an optical image of a subject are known. Among the various kinds of image sensors, a CCD image sensor is commonly used owing to its adjustable size, relatively high S/N ratio, sensitivity, and various other desirable attributes.
A CCD image sensor outputs pixel signals according to the amount of light received by the pixels by ordering a vertical CCD to receive signal charges generated by a plurality of pixels separately, by ordering the vertical CCD to transfer the signal charges to a horizontal CCD, and by ordering the horizontal CCD to transfer the signal charges to an output amplifier.
The vertical CCD happens to store the electrical charge which the vertical CCD generates itself when light is leaked to the vertical CCD, and from an electrical charge left upon transferring an electrical charge exceeding the transferring capacity, from an electrical charge leaked from a pixel, and so on. Such an electrical charge becomes noise in a signal charge, and should be discharged to display an accurate image.
Japanese Unexamined Patent Publication No. H04-356879 discloses the rapid discharge of electrical charges that remain in the vertical CCD before the vertical CCD receives and transfers signal charges from pixels.
The influence of noise can be reduced by the rapid discharge. However, the time required to discharge electrical charges from the vertical CCD is added to the time to complete a photographing operation from depressing a release button. Accordingly, the entire time to complete the photographing operation is undesirably prolonged. Especially in the case of continuous photographing, it is desirable to increase the amount of photographing per a certain time by completing the photographing operation rapidly.